Influence Of Single-ion Anisotropy Research Articles

Magnetic structures in R5Pt2In4 (R = Tb-Tm) investigated by neutron powder diffraction.

Results of the neutron powder diffraction measurements carried out for R5Pt2In4 (R = Tb-Tm) are reported. The compounds crystallize in an orthorhombic crystal structure of the Lu5Ni2In4-type with the rare earth atoms occupying three different sublattices. Neutron diffraction data reveal that at low temperatures the rare earth magnetic moments order below the critical temperature equal to 105, 93, 28, 12 and 3.8 K for R = Tb, Dy, Ho, Er and Tm, respectively. With decreasing temperature the rare earth magnetic moments at the 2a and 4g2 sites order first, while the moments at the 4g1 site order at lower temperatures. Ferrimagnetic order along the c axis, described by the propagation vector k1 = [0, 0, 0], develops in Tb5Pt2In4 below the Curie temperature (TC = 105 K). At lower temperatures, an antiferromagnetic component in the ab plane appears. The component is incommensurate with the crystal structure (k2 = [0, 0.66, ½]), but it turns into a commensurate one (k3 = [0, 0, ½]) with decreasing temperature. Antiferromagnetic order along the c axis, described by k4 = [½, 0, 0], is found in Dy5Pt2In4 below the Néel temperature (TN = 93 K). The k4-related component disappears below 80 K and the magnetic structure transforms into a ferro/ferrimagnetic one described by k1 = [0, 0, 0]. Further decrease in temperature leads to the appearance of an incommensurate antiferromagnetic component within the ab plane below 10 K (k2 = [0, 0.45, ½]), which finally turns into a commensurate one (k5 = [0, ½, ½]). In Ho5Pt2In4, a sine-modulated magnetic structure with moments parallel to the c axis (k6 = [⅓,0,0]) is observed below 28 K. With a decrease in temperature, new components, related to k1 = [0, 0, 0] (bc plane) and k4 = [½, 0, 0] (c axis), appear. The coexistence of two orderings - in the ab plane (k1 = [0, 0, 0]) and a modulated one with moments along the b axis (k7 = [kx, 0, 0]) - is found in Er5Pt2In4 below 12 K. Decreasing temperature leads to the order-order transformation of the k1-related component to another one with magnetic moments still constrained to the ab plane and preserved value of the propagation vector (i.e. k1 = [0, 0, 0]). Tm5Pt2In4 orders antiferromagnetically below TN = 3.8 K. Thulium magnetic moments lie in the ab plane, while the magnetic structure is described by k5 = [0, ½ , ½]. The direction of magnetic moments depends on the rare earth element involved and indicates an influence of single ion anisotropy resulting from interaction with the crystalline electric field.

Complex magnetic ordering in RE5Pd2In4 (RE = Tb-Tm) compounds investigated by neutron diffraction and magnetometric measurements

The RE5Pd2In4 (RE = Tb-Tm) compounds crystallize with the orthorhombic Lu5Ni2In4-type crystal structure (Pbam space group). In this work we report results of structural and magnetic studies by means of X-ray and neutron diffraction as well as dc and ac magnetometric data. Magnetic susceptibility and neutron diffraction data revealed rare-earth moments order at low temperatures with complex magnetic structures showing a cascade of temperature-induced transitions. The magnetic ordering temperatures are found to be 97, 88, 28.5, 16.5 and 4.3 K for RE = Tb, Dy, Ho, Er and Tm, respectively. Magnetic structures related to the propagation vector k→1=[0,0,0] are found just below the magnetic ordering temperatures in majority of the investigated compounds (RE = Tb-Er). Below the Curie temperature TC they have purely ferromagnetic character in Tb5Pd2In4 and Dy5Pd2In4. A ferrimagnetic order finally sets at lower temperatures in Dy5Pd2In4, while in Ho5Pd2In4 two magnetic phases related to k→1 are observed: the antiferromagnetic one (phase I) and the ferrimagnetic one (phase II, coexisting with phase I at lower temperatures). Er5Pd2In4 is a canted antiferromagnet with additional ferromagnetic component developing at lower temperatures. A purely antiferromagnetic component of magnetic structure with enlarged magnetic unit cell appears with decreasing temperature in Tb5Pd2In4 (k→2=[0,12,0] and k→3=[0,12,12]) while in Ho5Pd2In4 such component (k→4=[14,0,0]) is present within whole temperature range below the magnetic ordering temperature. Magnetic structure of Tm5Pd2In4, exceptionally, has no k→1 component, but is an antiferromagnetic incommensurate one related to two propagation vectors: k→5=[0.073(3),0.451(1),12] and k→6=[0,0.335(2),12]. In majority of the compounds (RE = Tb-Er) the first rare-earth 4g site (noted as 4g1) orders at lower temperature than two remaining sites (2a and 4g2). The direction of the magnetic moments depends on rare-earth element involved and indicates an influence of single-ion anisotropy in the crystalline electric field (CEF).

Dynamic phase transition and universality in a quasi 2D system: Bilayer Ising/Blume-Capel ferromagnet on a honeycomb lattice

Monte Carlo simulation technique is applied on a magnetic bilayer system composed of spin-1/2 Ising and spin-1 Blume-Capel spin variables distributed on a honeycomb lattice. Assuming an indirect exchange interaction between adjacent monolayers, we investigate the influence of single ion anisotropy and number of nonmagnetic layers between the magnetic sheets on the critical behavior of the system. Equilibrium phase diagram in a reduced pseudo critical temperature (Tc/J) versus reduced single ion anisotropy (DB/J) plane has been determined. In the presence of alternating magnetic field, dynamic phase transition properties have been elucidated. The form of the oscillating magnetic field is assumed to be in a square wave form. By performing a detailed finite-size scaling analysis, we have calculated the critical half period t1/2c at which the system undergoes a dynamic phase transition between dynamically ordered and disordered states. Extracted critical exponent ratios β/ν and γ/ν suggest that observed dynamic phase transition for the present multilayer system falls into the same universality class as the equilibrium two-dimensional Ising model.

Solitons in a one-dimensional ferromagnetic chain under the influence of single-ion anisotropy

Cnoidal wave solutions and soliton solutions in a one-dimensional ferromagnetic chain with anisotropy exchange interaction and single-ion anisotropy are obtained through travelling wave solution method and the influence of single-ion anisotropy on cnoidal waves and solitons is discussed. The results indicate that single-ion anisotropy makes the cnoidal waves and solitons easy to excite in an easy-plane ferromagnetic chain but difficult in an easy-axis one, and makes them more stable in the easy-axis ferromagnetic chain but less stable in the easy-plane one. The influence of single-ion anisotropy on soliton excitations in a one-dimensional isotropic ferromagnet is also discussed.

Magic angle line width in a one-dimensional Heisenberg magnet with single-ion anisotropy in the high-temperature limit

The EPR line width and the dynamical shift of the line position in a one-dimensional Heisenberg magnet with the external magnetic field making the magic angle (54.7°) with the chain axis are calculated. Both the line width and the dynamical shift have a characteristic frequency dependence (∝ ω− 1 2 ). The second moment and fourth moment, with and without exchange, of the absorption line are calculated explicity. From this it can be concluded that the distribution of the internal dipolar fields is strongly non-gaussian. The influence of single-ion anisotropy is shown to be an additional broadening or a narrowing of the resonance line depending on the sign of the interaction. Single-ion anisotropy does not change the characteristic line shape and angular dependence of a one-dimensional Heisenberg magnet.